The present invention relates generally to the field of gas appliance monitoring systems. More particularly, the present invention relates to a gas appliance monitoring system and alarm timing mechanism for automatically detecting and alerting to a “gas-out” condition of a gas appliance during operation, and/or for alerting to the presence of sustained gas flow after a predetermined period of time.
Gas-operated appliances, such as barbecue grills, deck heaters, fireplaces, and the like have become commonplace. The availability of either natural or propane gas as a fuel makes these appliances particularly convenient. However, it is commonplace for the users of such appliances to (1) run out of gas during operation of the appliance, and/or (2) accidentally leave the appliance turned on long after their intended period of use. It is most inconvenient and irritating when the gas supply expires during use of the appliance. In the case of a barbecue grill, the user will generally have no idea as to how long the event has occurred, possibly ruining the meal. Leaving an appliance on too long is also frustrating, as this leads to an expensive waste of fuel, the inconvenience of refilling portable gas tanks, and a considerable safety hazard. The problem is magnified when the appliances are plumbed directly to the available natural gas supply or household propane tank.
With millions of gas grills and other gas appliances being sold around the world each year, clearly an effective signaling/safety device capable of detecting and alerting to a gas-out condition during operation is desirable. It would also be beneficial for such a system to alert for the presence of sustained gas flow after a predetermined period of time. Automatic versus manual operation of such a system is also deemed desirable, in that in that the user should not have to enable it at the beginning of the grilling cycle, or disable it at the end. A system that is not automatic is less likely to get used, and an automatic system can provide the best power conservation, which is important in a battery powered system.
Others have heretofore attempted to provide alerts of gas-out conditions of a gas appliance during use. One known system utilizes a single sensor to monitor gas supply pressure to alert of low fuel, but this system must be manually activated upon each usage. Automatic operation with such a single sensor system is not possible, as there is no way for the system to know that the appliance is actually operating (i.e., gas is flowing). Since these systems lack a gas flow sensor or knob position/gas valve activation sensor, they cannot be automatically activated or deactivated when the appliance is turned on or off by simply utilizing the appliance controls.
In U.S. Pat. Nos. 5,003,960 and 5,033,449, a device is disclosed which electronically weighs the tank and then calculates and displays the amount of time remaining before gas expiration. An alarm is set off when the calculated time is low enough and/or a flame detector senses the flame has stopped while the tank weight is low. This is a potentially very dangerous approach, however, as the system cannot discern a situation where the flame has stopped and the gas is still flowing. A flame detector does provide a positive indication of gas flow, but the converse is not true, i.e., it cannot provide a positive indication that the flow of gas has stopped.
From the above, it is evident there is a distinct need for a gas appliance monitoring system which will automatically detect and alert to gas-out conditions during appliance operation. It would also be beneficial if such a system could also detect the presence of sustained gas flow after a predetermined period of time, without the need for manual system reset. Obviously, it would be desirable to offer these features, either alone or combined, in both aftermarket and original equipment manufacturer (OEM) versions. Finally, any such system must also provide for reliable detection of appliance operation to avoid false alarm situations.
It is therefore an object of the present invention to provide an OEM and aftermarket gas appliance monitoring system which will automatically and reliably detect and alert to gas-out conditions during appliance operation, and to the presence of sustained gas flow after a predetermined period of time.
It is also an object of the present invention to detect gas-out conditions of an appliance without the use of pressure sensors, tank scales, or a combination thereof, by utilizing a highly sensitive flow indicator/switch to automatically detect the difference in gas flow characteristics between an appliance that is intentionally turned off versus an appliance that experiences a gas-out condition during operation.
It is another object of the present invention to provide a novel configuration of a piston-type positive displacement fluid flow indicator/switch which is highly sensitive and useful for detecting the flow of gas, and thus operation of the appliance, in low flow applications, such as with gas grills and the like, and which will function accurately in such a gas appliance monitoring system without significant pressure loss, flow restriction or piston oscillation.
It is still a further object of the present invention to provide a novel and useful fluid flow indicator which (1) utilizes multiple detection sensors/switches to monitor timing differences in piston movement under different operating conditions to determine and alert for gas-out conditions during operation, and/or (2) includes a timer, alarm system and optional activity sensor for alerting to the presence of sustained gas flow after a predetermined period of time.